A conventional double-nut cooling ball screw as disclosed in Taiwanese Utility Model No. M444445 generally includes a front nut member having spacedly displaced cooling channels, a rear nut member having spacedly displaced cooling channels, a preload member fittingly disposed between the front and rear nut members and having through holes for communicating the cooling channels in the front and rear nut members, and a plurality of sealing members each disposed at the juncture of the through hole and the cooling channel of a respective one of the front and rear nut members, such that a coolant can circulate in the cooling channels to cool the ball screw.
Such cooling ball screw is relatively inconvenient to assemble. The sealing members are firstly placed at ends of the cooling channels, and the front and rear nut members are then threadedly engaged with a threaded shaft to be adjoined to each other to sandwich the preload member. During the threaded movement, the sealing members are easily separated from the front and rear nut members. Moreover, the sealing members are easily scratched by the preload member, which may weaken or lose its sealing effect.
Another conventional ball screw as disclosed in U.S. Pat. No. 9,133,921 generally includes a threaded shaft, two nuts threadedly engaging with the threaded shaft, a spacer tightly sandwiched between the nuts and having through holes, and two ring-shaped sealing members connected between the nuts and inserted into the through holes. Each nut has two counterbores, each of which extends axially from a connecting end thereof to sealingly receive an end portion of the sealing member. The counterbore (a receiving counterbore) of one of the nuts has a depth sufficient to accommodate the entire of the sealing member. The through holes in the nuts are connected through the through holes in the spacer and the sealing members, such that a coolant can circulate therein to cool the ball screw.
However, an additional tool is required to conduct assembly. Following accommodation of the sealing members in the receiving counterbores, the nuts and the spacer are mounted on the threaded shaft. A round bar (a pressing tool) is inserted into the through hole in the nut to press each of the sealing members to another counterbore, which renders the assembly process cumbersome.